In manufacturing tanks such as air tanks, other compressed gas tanks and fuel tanks, it is necessary to provide fluid couplings for dispensing the contents of the tanks for various uses such as operating air brakes or pneumatic tools, or for powering internal combustion engines used in vehicles, or for other purposes. In addition, it may be necessary to attach instruments such as pressure and temperature indicators to these tanks. Typically, a tank may have one or more sites at which a fluid coupling is attached. These sites may vary according to a customer's order or according to the purpose for which the tank is used.
It is current practice to punch holes through the sheet metal used for forming tank walls before the tank walls are fabricated into completely enclosed tanks. From a practical standpoint, it is impossible to effectively punch holes in a closed tank because there is no access to the interior of the tank for inserting a die against which the punch acts when making the holes.
It is not unusual for customers to relocate holes for fittings in order to make the tanks more compatible with altered design criteria. This requires the fabricator of the tank to relocate holes for fittings on a flat blank before the tank is shaped. After the tank has been shaped, the hole may not occur in the finally formed tank where it was supposed to occur or the customer may change his or her mind as to the desired location. Normally, it is not just one tank, but many tanks which end up with holes not located where the customer has either specified or would later prefer. Accordingly, it is frequently desirable to have a completed tank for the customer to inspect prior to making holes for fittings. Heretofore, this has not necessarily been practical because holes would have had to be drilled after tanks were enclosed which would result in debris accumulating in the tanks. Debris in a tank can damage equipment being operated or powered by the fluid dispensed from the tank.
Another problem has arisen with the advent of "quick-connect" couplings in which, instead of threading a coupling to a tank, couplings are simply pushed home to seat within a bushing installed on the tank. A prior art method of installing a bushing on a tank is to weld the bushing to the exterior of the tank in order to provide a smooth bore into which the quick-connect coupling is inserted. It is very important to inspect the weld to make sure that the weld is fluid-tight and that the weld is sound, otherwise, there is a possibility of fluid leaking or, in the case of tanks containing compressed gas, the possibility of the weld blowing out. Inspecting welds for integrity is not an inexpensive, risk-free task.
In view of the aforementioned considerations, there is a need for improvement in techniques for providing tanks with holes for fittings.